U.S. patent application number 12/447722 was filed with the patent office on 2010-03-18 for method of assembling a light element module and light element module assembly.
Invention is credited to Patrick J. Hughes, John C. Jackson.
Application Number | 20100065724 12/447722 |
Document ID | / |
Family ID | 37546154 |
Filed Date | 2010-03-18 |
United States Patent
Application |
20100065724 |
Kind Code |
A1 |
Hughes; Patrick J. ; et
al. |
March 18, 2010 |
METHOD OF ASSEMBLING A LIGHT ELEMENT MODULE AND LIGHT ELEMENT
MODULE ASSEMBLY
Abstract
A method is provided of at least partly assembling a light
sensor module having at least one light sensing element optically
coupled to a further optical element, for receiving light
therefrom. The method comprises coupling the at least one light
sensing element to an intermediate layer, wherein the intermediate
layer is adapted to provide at least a predetermined level of
optical coupling between the optical element and the at least one
light sensing element when assembled by subsequently coupling, for
example as part of a separate method, the intermediate layer to the
optical element, with the intermediate layer being arranged between
the optical element and the at least one light sensing element. An
optical element other than a light sensing element, for example a
light source element, can be used in place of the or each light
sensing element, with in that case the or each optical element
providing light to the further optical element rather than
receiving light therefrom. Thus, the method can relate to an
optical assembly in general rather than to a light sensor module
assembly in particular.
Inventors: |
Hughes; Patrick J.; (Cork,
IE) ; Jackson; John C.; (Cork, IE) |
Correspondence
Address: |
MARK D. SARALINO (GENERAL);RENNER, OTTO, BOISSELLE & SKLAR, LLP
1621 EUCLID AVENUE, NINETEENTH FLOOR
CLEVELAND
OH
44115-2191
US
|
Family ID: |
37546154 |
Appl. No.: |
12/447722 |
Filed: |
October 29, 2007 |
PCT Filed: |
October 29, 2007 |
PCT NO: |
PCT/EP07/61619 |
371 Date: |
June 24, 2009 |
Current U.S.
Class: |
250/216 ;
29/592.1 |
Current CPC
Class: |
G01T 1/1644 20130101;
Y10T 29/49002 20150115; G01T 1/2018 20130101 |
Class at
Publication: |
250/216 ;
29/592.1 |
International
Class: |
G01J 1/42 20060101
G01J001/42 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 30, 2006 |
GB |
0621495.1 |
Claims
1. A method of assembling a light sensor module having at least one
light sensing element optically coupled to a further optical
element, for receiving light therefrom, the method comprising: a
first step of coupling the at least one light sensing element to an
intermediate layer; and a second step, following after the first
step, of coupling the intermediate layer to the optical element,
such that the intermediate layer is arranged between the optical
element and the at least one light sensing element; wherein the
intermediate layer is adapted to provide at least a predetermined
level of optical coupling between the optical element and the at
least one light sensing element.
2. A method as claimed in claim 1, wherein the or each of the at
least one light sensing element has a respective light input
surface arranged to face the intermediate layer.
3. A method as claimed in claim 1, wherein the intermediate layer
is so adapted by being thin.
4. A method as claimed in claim 1, wherein the intermediate layer
has a thickness of less than 500 .mu.m.
5. A method as claimed in claim 4, wherein the intermediate layer
has a thickness of less than 100 .mu.m.
6. A method as claimed in claim 5, wherein the intermediate layer
has a thickness of less than 50 .mu.m.
7. A method as claimed in claim 1, wherein the intermediate layer
is so adapted by being sufficiently optically transparent to
provide the predetermined level of optical coupling.
8. A method as claimed in claim 1, wherein the intermediate layer
is so adapted by comprising at least one aperture formed therein,
and wherein the first step comprises arranging the or each of the
at least one sensing element over a corresponding respective
aperture.
9. A method as claimed in claim 8, wherein sidewalls of the at
least one aperture are angled and/or metallised to improve the
optical coupling.
10. A method as claimed in claim 8, comprising filling the at least
one aperture with a material having a refractive index selected to
improve the optical coupling.
11. A method as claimed in claim 1, wherein the intermediate layer
is provided with at least one alignment feature to enable alignment
of the at least one sensing element on the intermediate layer.
12. A method as claimed in claim 11, wherein the intermediate layer
is so adapted by comprising at least one aperture formed therein,
and wherein the first step comprises arranging the or each of the
at least one sensing element over a corresponding respective
aperture and wherein the at least one alignment feature comprises
the at least one aperture.
13. A method as claimed in claim 12, wherein the optical element is
at least partly segmented into at least one region, and wherein the
or each of the at least one aperture is arranged to align with a
corresponding respective region of the optical element when
assembled, thereby achieving alignment between the at least one
region and the at least one sensing element when assembled.
14. A method as claimed in claim 1, wherein the intermediate layer
comprises one or more embedded optical layers, such as waveguides
and optical elements such as gratings or mirrors, to couple,
transport and/or redirect light between different light sensing
elements.
15. A method as claimed in claim 1, wherein the intermediate layer
comprises a substantially planar film.
16. A method as claimed in claim 1, wherein the intermediate layer
comprises a polymer material.
17. A method as claimed in claim 1, wherein the intermediate layer
is flexible.
18. A method as claimed in claim 17, wherein the intermediate layer
is at least partly stiffened, for example around the periphery of
circuitry, to provide specific areas of rigidity where needed.
19. A method as claimed in claim 17, wherein the optical element
comprises a curved surface, and the method comprising coupling the
intermediate layer to the optical element over at least part of the
curved surface, the flexibility of the intermediate layer allowing
it to conform to the curved surface.
20. A method as claimed in claim 19, comprising altering the shape
of the curved surface after coupling the intermediate layer to the
optical element, with the intermediate layer retaining its
conformance to the curved surface.
21. A method as claimed in claim 1, wherein the intermediate layer
is substantially rigid.
22. A method as claimed in claim 1, wherein the intermediate layer
is formed of material such as PCB, Silicon, glass, polyimide or
dielectric film.
23. A method as claimed in claim 1, wherein metal tracking is
formed over the intermediate layer, and wherein the first step
comprises electrically coupling the at least one sensing element to
the metal tracking.
24. A method as claimed in claim 23, wherein the metal tracking is
formed by one or more levels of metal, on one or both sides of the
intermediate layer.
25. A method as claimed in claim 23, wherein the metal tracking
forms a printed circuit on the intermediate layer.
26. A method as claimed in claim 23, wherein the metal tracking is
arranged to allow each of the plurality of sensing elements to be
addressed individually.
27. A method as claimed in claim 23, wherein the metal tracking is
arranged to allow each of the plurality of sensing elements to be
addressed collectively.
28. A method as claimed in claim 1, wherein additional circuitry
and/or electrical components is/are provided on the intermediate
layer.
29. A method as claimed in claim 1, wherein the intermediate layer
is provided with single or multiple bondpad sites.
30. A method as claimed in claim 1, wherein the intermediate layer
is provided with a patterned light reflective surface arranged to
face the optical element to reflect light back towards the optical
element that does not fall on a respective active area of the at
least one light sensing element.
31. A method as claimed in claim 1, wherein the intermediate layer
is adapted to enable the coupling and/or attachment of fibres,
waveguides, lights cones and the like, so as to be accurately
aligned and connected to the at least one light sensing
element.
32. A method as claimed in claim 1, wherein the intermediate layer
comprises at least one perforated structure with a pedestal and/or
stand-off to enable direct integration of a coupling element such
as a fibre.
33. A method as claimed in claim 1, wherein the intermediate layer
comprises at least one adhesive site or appropriate mounting
feature to enable alignment and/or locking of the at least one
sensing element on the intermediate layer.
34. A method as claimed in claim 1, wherein a plurality of sensing
elements are arranged on the intermediate layer in a tiled or array
configuration.
35. A method as claimed in claim 1, wherein the or each element
comprises Silicon Photomultiplier circuitry.
36. A method as claimed in claim 1, wherein the optical element is
selected from: fibre optics, scintillators, photonic crystals,
quantum dots, lasers, holy fibres, and waveguides.
37. A method as claimed in claim 1, wherein the second step is not
carried out as part of the claimed method, only subsequently.
38. A method as claimed in claim 1, wherein the predetermined level
of optical coupling is at least 75%.
39. A method as claimed in claim 38, wherein the predetermined
level of optical coupling is at least 85%.
40. A method as claimed in claim 1, wherein the intermediate layer
comprises an adhesive layer for mechanically attaching the or each
light sensing element mounted on the intermediate layer to the
further optical element.
41. A method of at least partly assembling a light sensor module
having at least one light sensing element optically coupled to a
further optical element, for receiving light therefrom, the method
comprising: coupling the at least one light sensing element to an
intermediate layer, wherein the intermediate layer is adapted to
provide at least a predetermined level of optical coupling between
the optical element and the at least one light sensing element when
assembled by subsequently coupling, as part of a separate method,
the intermediate layer to the optical element, with the
intermediate layer being arranged between the optical element and
the at least one light sensing element.
42. A light sensor module assembly comprising at least one light
sensing element optically coupled to a further optical element, for
receiving light therefrom, wherein the at least one light sensing
element is coupled to an intermediate layer, and the intermediate
layer is coupled to the optical element, such that the intermediate
layer is arranged between the optical element and the at least one
light sensing element, and wherein the intermediate layer is
adapted to provide at least a predetermined level of optical
coupling between the optical element and the at least one light
sensing element.
43. A light sensor module assembly as claimed in claim 42, wherein
the optical element comprises a curved surface, and wherein the
intermediate layer is coupled to the optical element over at least
part of the curved surface, the intermediate layer being flexible
so as to allow it to conform to the curved surface.
44. A light sensor module assembly comprising at least one light
sensing element coupled to an intermediate layer, wherein the
intermediate layer is adapted to provide at least a predetermined
level of optical coupling between the at least one light sensing
element and a further optical element when the intermediate layer
is subsequently coupled to the further optical element, with the
intermediate layer arranged between the optical element and the at
least one light sensing element, the at least one sensing element
receiving light in use from the further optical element.
45. A method or module as claimed in claim 1, in which an optical
element other than a light sensing element, for example a light
source element, is used in place of the or each light sensing
element, with the direction of light transferral between the or
each optical element and the further optical element being
construed accordingly, the method or module thereby relating to an
optical assembly in general rather than to a light sensor module
assembly in particular.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method of assembling a
light module and a light module when so assembled.
DISCUSSION OF RELATED ART
[0002] Avalanche Photodiode (APD) sensors are commonly used to
detect extremely small amounts of light across the whole spectrum
including UV, visible or IR radiation. Typically, a photodiode is
biased in avalanche mode, which results in a single incident photon
of light producing a large number of electron hole pairs, i.e. a
large current. This results in a low-light signal producing an
amplified and readable electrical signal proportional to the input
light signal, i.e. an analogue electrical output. Typical
amplification or gain for normal APDs is measured in the tens to
hundreds.
[0003] This is to be contrasted with Geiger-mode operation of
photodiodes. In Geiger mode, the diode junction is reverse-biased
above the breakdown voltage for the diode. An incident light photon
will cause an uncontrolled avalanche of electron-hole pairs, and
hence a large spike of current. A quench circuit detects the surge
in current caused by this breakdown and reduces the reverse bias
voltage across the junction, which in turn stops the breakdown, and
thereby stops the current. The effect is a pulse of current for
each photon. Typical amplification or gain values for photodiodes
operating in Geiger mode is >10.sup.5.
[0004] A Silicon Photomultiplier (SiPM) is a relatively new sensor
concept, and is described in: (a) Z. Y. Sadygov et al., "Avalanche
Semiconductor Radiaton Detectors", Trans. Nucl. Sci. Vol. 43, No. 3
(1996) 1009; and (b) V. Saveliev, "The Recent Development and Study
of Silicon Photomultiplier", Nucl. Instr. Meth. A 535 (2004)
528-532.
[0005] A SiPM uses an array of photodiodes operating in Geiger mode
and sums the electrical output of all the diodes. The net result is
a series of pulses (from the diodes that have detected a photon)
being added together. As individual diodes detect photons the
summed output will increase or decrease. This produces an analogue
electrical output which is proportional to the number of photons
incident on the total sensor. The gain in this case is still
>10.sup.5.
[0006] There are three different categories of existing technology
that produce an amplified analogue electrical output signal that is
proportional to the optical signal, as set out below.
[0007] (a) Photomultiplier Tubes (PMTs). These are the traditional
solution for applications requiring large area and large gain
sensors. They are based on similar technology to that used in early
glass tube transistors in the 1950s, and rely on a photocathode to
convert a photon into a photoelectron and a separate dynode chain
under high bias to produce amplification of the photoelectron.
Their disadvantages include that they are bulky, cannot be
miniaturised, generally have a slow timing response (except for
high-end, and expensive, microchannel plate detector type PMTs,
which can exhibit picosecond timing resolution), require high bias
operation (typically from 500 V to 2000 V), can be damaged when
exposed to ambient light, have low Quantum Efficiency, and
importantly for many applications have high sensitivity to magnetic
environments. They are, however, large area (typically 1 to 2
inches) and provide a high gain to the collected photoelectrons
(typically of the order of 10.sup.6).
[0008] (b) Normal APDs. The basic operation of these devices has
been briefly explained above. This type of device has been the only
solid-state APD solution until recently, and has been applied in
many applications. However, as mentioned above, the gain is low
(typically 10 to 200), and it is difficult to achieve a stable high
value of gain. It is also difficult to produce large area devices
that do not have large dark current.
[0009] (c) SiPMs--Silicon Photomultipliers. These devices are
mentioned briefly above. In particular, their gain is very high,
and the size of the sensor can also be made relatively large, for
example up to 4 mm.sup.2. For applications above this size, there
are a number of technical issues. It is important to have
uniformity on the breakdown voltage across the large number of
diodes/pixels in a SiPM, and the wafer processing control required
to achieve this can become difficult for larger sensors.
[0010] Applications for photo-detection systems include
spectro-photometric systems, nuclear medical systems, biomedical
systems, microarray scanners, biodiagnostics systems, and high
energy physics. Each of these applications requires that a detector
or detector arrays be closely coupled with scintillators or other
light sources, in addition to the integration of electrical contact
to the detectors and connections to external electronics. The
detection systems for these applications require high gain, large
area optical detectors, and accordingly the current optical
detector market is dominated by Photomultiplier Tubes (PMTs).
[0011] Typically, the large sensitive area of the PMT detector
makes it ideal for many applications where there is a large area
that needs to be imaged or that photons are coming from a large
diffuse source. In these cases, it is difficult to use small area
detectors as there are large losses in the optical systems that are
required to couple photons onto the detector. For these large
detection applications, a large area detector is required. Many of
these applications also require the use of scintillators to convert
high energy photons into lower energy photons suitable for
detection with commonly-used detectors. Ideally, detection of high
energy particles could be performed directly by the detector
itself, but the energy of the photons under detection are often of
the order of keV which are difficult to detect with present
state-of-the-art detectors. For these applications, a scintillator
is required for photon conversion and it must be directly coupled
onto the detector to minimise photon loss. Several applications
that require large area detectors are described below by way of
example.
[0012] In nuclear medicine, radiological imaging techniques are
widely employed to study body functions (human and small animal)
such as blood flow, metabolic processes and anatomical features. To
carry out a nuclear scan, small tracer amounts of radioisotopes are
administered to patients and sophisticated imaging systems perform
cross section and 3D images. Current imaging techniques include:
Single photon emission computed tomography (SPECT); Positron
Emission Tomography (PET for humans & animals); and MRI
(magnetic resonance imaging).
[0013] Recent years have seen the introduction of multi-modality
imaging. The primary benefit of the use of two simultaneous scans
is the acquisition of two data sets that can be exactly
superimposed, spatially, and to some extent, temporally. This is
most beneficial when the two data sets yield different and
complimentary information, such as the functional (e.g. metabolic)
information from PET with the higher resolution anatomical detail
given by CT (Computed Tomography). CT data can also be used for the
attenuation correction of PET data and now combined PET/CT systems
are available commercially. (For example see T Beyer et al Journal
of Nuclear Medicine, Vol 41, Issue 8 1369-1379, 2000; "A combined
PET/CT scanner for clinical oncology".)
[0014] Similarly, the possibility of simultaneous PET and MRI is
currently being pursued. Although this is substantially less
straightforward than the integration of PET/CT, the gains are
deemed to be worth the effort. Small prototypes have been built and
used as demonstrators, but no full system currently exists. A full
system based on PMTs (like the demonstrator) is unlikely to be
commercially viable due to magnetics incompatibility.
[0015] Another desirable feature for future PET systems is that of
time-of-flight (ToF). This is based upon having a very good
timing-resolution detection system, such that the arrival times of
the two 511 keV photons are recorded with sufficient accuracy to
enable one to narrow down the range of possible origin points of
the photons. ToF is unlikely to be good enough to directly improve
the spatial resolution of the system, but by eliminating sources of
noise from outside the area of interest, one can reconstruct a
better quality image. Therefore, a detector with very fast timing,
would enable the development of such systems.
[0016] In addition, PET detector modules comprise PMTs coupled to
respective scintillators. Scintillators are materials that emit
visible or near visible light when energy is absorbed from ionising
radiation such as gamma rays. Typically, scintillator materials
include LSO, LYSO, BaF.sub.2 and BGO crystals and have been used to
count and image radioisotopes when coupled to PMTs.
[0017] In PET detector modules, the decay of the radioisotope
produces 2 antiparallel gamma rays, each at 511 keV. The most
efficient way of imaging is to enclose the patient with a ring of
scintillator detectors with each detector in electronic coincidence
with those on the opposite side of the patient. When a pair of
photon detectors simultaneously detect 511 key energy an
annihilation event has occurred. Multiple detector rings are
stacked on top of one another to obtain a 3D image.
[0018] The detector module consists of a block detector. Typically,
the scintillator detector consists of a block of scintillator which
is partially cut to create a N.times.N array of quasi-independent
crystals (pixellated crystals) that are grouped together and
coupled to PMTs. FIG. 1 of the accompanying drawings shows a
conventional Scintillator-to-PMT PET detection system. A PMT used
in these applications is typically of the order of 1'' to 1.5'' in
diameter (or 1''.times.1'' to 1.5''.times.1.5'').
[0019] PMTs are widely used my many high energy physics
experiments, forming the basis of a large amount of the
instrumentation. Many of the detectors for the high energy
particles produced in these experiments are composite detectors,
being formed of a scintillator and photodetector. The scintillator
acts as a converter medium, absorbing the high energy particles and
photons and emitting lower energy, visible photons. This light is
then measured by the photodetector. Depending of the chosen
configuration of these two elements, position, energy and timing
information can be obtained. Typically these experiments require
large detectors, surrounding the `vertex point` where the two
particle beams collide. Sometimes, the area of photodetector
required to readout a given scintillator volume is reduced by using
fibres that guild the light onto a PMT.
[0020] The compatibility of PMT with MRI systems is impractical and
requires the development of an alternative magnetic insensitive
detectors technology for multi-modal systems. One promising
alternative for PET systems is the Silicon Photomultiplier (SiPM)
mentioned above; for example, see N Otte et al "The SiPM A new
Photon Detector for PET", Nuclear Physics B (Proc. Suppl.) 150
(2006) 417-420. SiPM detectors are attractive to PET systems
because they allow one-to one coupling to small crystals allowing
for better overall spatial resolution. In addition, the transit
time spread of SiPM detectors is small (e.g. 100 ps) which is
important for PET scanners which use time of flight (TOF)
information as the coincidence time resolution of the system
enables enable reduction is statistical noise in image
reconstructions.
[0021] In addition, for good spatial resolution in PET modules, it
is important to be able to measure the identity of the pixellated
crystal but also the depth of interaction within that crystal.
Several approaches to measuring interaction depth are possible.
These include: (a) stratified layers of different scintillator with
different decay times; (b) light sharing approach where each
scintillator element is attached to two detectors at opposing ends
of the crystal; and (c) stacking of image planes of scintillator
and detectors.
[0022] To improve the design of calorimeters in HEP (High Energy
Physics) applications, greater integration of the different
detection systems are needed. SiPM technology is a promising
candidate to integrate directly large area arrays of detectors
directly to scintillators in magnetic environments typically in the
region of 2-5T, see for example V D Kovaltchouk, G J Lolos, Z
Papandreou and K Wolbaum "Comparison of a silicon photomultiplier
to a traditional vacuum photomultiplier", Nuclear Instruments and
Methods in Physics Research Section A: Accelerators, Spectrometers,
Detectors and Associated Equipment, Volume 538, Issues 1-3, 11 Feb.
2005, Pages 408-415.
[0023] The above two examples highlights the current constraints
with PMT when magnetic environments are used. The current solutions
to overcome the practical issues with PMT include shielding, remote
housing of PMTs from source and coupling via optical fibers are not
adequate and hence SiPM technology is attractive.
[0024] As mentioned previously, the Silicon Photomultiplier (SiPM)
is an extension of the concept of the Geiger-mode avalanche
photodiodes (APD) to give an output signal proportional to the
input photon flux, by using a parallel array of such devices with
multiplexed output. In this way, the total device behaves like an
`analogue` device for photon fluxes, where the number of pixels
activated, and hence the size of the output current, is directly
proportional to the number of incident photons.
[0025] The SiPM detector has performance characteristics comparable
to PMT devices and overcomes many of their operational limitations
including robustness, magnetic sensitivity, ambient light
sensitivity and high bias voltage requirement. In addition, the
main benefits include: [0026] compact, small form factor sensors
and front end electronics compared to PM tubes, [0027] immune to
fluctuating magnetic fields, no high-voltage supply and low power
consumption, [0028] high quantum efficiency and timing response,
[0029] low excess noise.
[0030] SiPM detectors are currently limited to detector sizes of
the order to several millimeters square. To compete with PMT, large
area detection comparable to the typical PMT area of .about.1''
sizes is required. At present, large area single chip monolithic
solutions are not available with SiPM technology.
[0031] It is desirable to address the scaling of individual small
PM detectors to tile across a large area to develop large area
detection. This is taught to some extent in our co-pending
PCT/GB2006/050123, but particular issues need to be addressed when
considering a one-to-one coupling between the SiPM detectors and
further optical elements like scintillators or optical source
blocks, for example in applications including but not limited to
those described above.
[0032] Radiation detectors mounted on a substrate are disclosed in
A Jaksic, K Rodgers, C Gallagher, and P J Hughes, "Use of RADFETs
for Quality Assurance of Radiation Cancer Treatments", PROC. 25th
International Conference On Microelectronics (Miel 2006), Vol 2,
Belgrade, Serbia And Montenegro, May, 2006.
SUMMARY
[0033] According to a first aspect of the present invention there
is provided a method of assembling a light sensor module having at
least one light sensing element optically coupled to a further
optical element, for receiving light therefrom, the method
comprising: a first step of coupling the at least one light sensing
element to an intermediate layer; and a second step, following
after the first step, of coupling the intermediate layer to the
optical element, such that the intermediate layer is arranged
between the optical element and the at least one light sensing
element; wherein the intermediate layer is adapted to provide at
least a predetermined level of optical coupling between the optical
element and the at least one light sensing element.
[0034] The or each of the at least one light sensing element may
have a respective light input surface arranged to face the
intermediate layer.
[0035] The intermediate layer may be so adapted by being thin.
[0036] The intermediate layer may have a thickness of less than 500
.mu.m.
[0037] The intermediate layer may have a thickness of less than 100
.mu.m.
[0038] The intermediate layer may have a thickness of less than 25
.mu.m.
[0039] The intermediate layer may be so adapted by being
sufficiently optically transparent to provide the predetermined
level of optical coupling.
[0040] The intermediate layer may be so adapted by comprising at
least one aperture formed therein, and the first step may comprise
arranging the or each of the at least one sensing element over a
corresponding respective aperture.
[0041] Sidewalls of the at least one aperture may be angled and/or
metallised to improve the optical coupling.
[0042] The method may comprise filling the at least one aperture
with a material having a refractive index selected to improve the
optical coupling.
[0043] The intermediate layer may be provided with at least one
alignment feature to enable alignment of the at least one sensing
element on the intermediate layer.
[0044] The at least one alignment feature may comprise the at least
one aperture.
[0045] The optical element may be at least partly segmented into at
least one region, and the or each of the at least one aperture may
be arranged to align with a corresponding respective region of the
optical element when assembled, thereby achieving alignment between
the at least one region and the at least one sensing element when
assembled.
[0046] The intermediate layer may comprise one or more embedded
optical layers, such as waveguides and optical elements such as
gratings or mirrors, to couple, transport and/or redirect light
between different light sensing elements.
[0047] The intermediate layer may comprise a substantially planar
film.
[0048] The intermediate layer may comprise a polymer material.
[0049] The intermediate layer may be flexible.
[0050] The intermediate layer may be at least partly stiffened, for
example around the periphery of circuitry, to provide specific
areas of rigidity where needed.
[0051] The optical element may comprise a curved surface, and the
method may comprise coupling the intermediate layer to the optical
element over at least part of the curved surface, the flexibility
of the intermediate layer allowing it to conform to the curved
surface.
[0052] The method may comprise altering the shape of the curved
surface after coupling the intermediate layer to the optical
element, with the intermediate layer retaining its conformance to
the curved surface.
[0053] The intermediate layer may be substantially rigid.
[0054] The intermediate layer may be formed of material such as
PCB, Silicon, glass, polyimide or dielectric film.
[0055] Metal tracking may be formed over the intermediate layer,
and the first step may comprise electrically coupling the at least
one sensing element to the metal tracking.
[0056] Metal tracking may be formed by one or more levels of metal,
on one or both sides of the intermediate layer.
[0057] The metal tracking may form a printed circuit on the
intermediate layer.
[0058] The metal tracking may be arranged to allow each of the
plurality of sensing elements to be addressed individually.
[0059] The metal tracking may be arranged to allow each of the
plurality of sensing elements to be addressed collectively.
[0060] Additional circuitry and/or electrical components may be
provided on the intermediate layer.
[0061] The intermediate layer may be provided with single or
multiple bondpad sites.
[0062] The intermediate layer may be provided with a patterned
light reflective surface arranged to face the optical element to
reflect light back towards the optical element that does not fall
on a respective active area of the at least one light sensing
element.
[0063] The intermediate layer may be adapted to enable the coupling
and/or attachment of fibres, waveguides, lights cones and the like,
so as to be accurately aligned and connected to the at least one
light sensing element.
[0064] The intermediate layer may comprise at least one perforated
structure with a pedestal and/or stand-off to enable direct
integration of a coupling element such as a fibre.
[0065] The intermediate layer may comprise at least one adhesive
site or appropriate mounting feature to enable alignment and/or
locking of the at least one sensing element on the intermediate
layer.
[0066] A plurality of sensing elements may be arranged on the
intermediate layer in a tiled or array configuration.
[0067] The or each element may comprise Silicon Photomultiplier
circuitry.
[0068] The optical element may be selected from: fibre optics,
scintillators, photonic crystals, quantum dots, lasers, holy
fibres, and waveguides.
[0069] The second step may not carried out as part of a method
according to the invention, only subsequently.
[0070] The predetermined level of optical coupling may be at least
75%. The predetermined level of optical coupling may be at least
85%. However, the coupling efficiency need not be high. It can be
determined according to the requirements of the intended
application. Indeed, the coupling efficiency could be rather low,
so long as the sensitivity is high enough to allow the signal to be
detected. For example, there are cases where the coupling
efficiency might intentionally be lowered if the optical source is
emitting too much light and saturating the detector.
[0071] The intermediate layer may be adapted to include electronic
circuitry.
[0072] The intermediate layer may comprise an adhesive layer for
mechanically attaching the or each light sensing element mounted on
the intermediate layer to the further optical element.
[0073] According to a second aspect of the present invention there
is provided a method of at least partly assembling a light sensor
module having at least one light sensing element optically coupled
to a further optical element, for receiving light therefrom, the
method comprising: coupling the at least one light sensing element
to an intermediate layer, wherein the intermediate layer is adapted
to provide at least a predetermined level of optical coupling
between the optical element and the at least one light sensing
element when assembled by subsequently coupling, as part of a
separate method, the intermediate layer to the optical element,
with the intermediate layer being arranged between the optical
element and the at least one light sensing element.
[0074] According to a third aspect of the present invention there
is provided a light sensor module assembly comprising at least one
light sensing element optically coupled to a further optical
element, for receiving light therefrom, wherein the at least one
light sensing element is coupled to an intermediate layer, and the
intermediate layer is coupled to the optical element, such that the
intermediate layer is arranged between the optical element and the
at least one light sensing element, and wherein the intermediate
layer is adapted to provide at least a predetermined level of
optical coupling between the optical element and the at least one
light sensing element.
[0075] The optical element may comprise a curved surface, and the
intermediate layer may be coupled to the optical element over at
least part of the curved surface, the intermediate layer being
flexible so as to allow it to conform to the curved surface.
[0076] According to a fourth aspect of the present invention there
is provided a light sensor module assembly comprising at least one
light sensing element coupled to an intermediate layer, wherein the
intermediate layer is adapted to provide at least a predetermined
level of optical coupling between the at least one light sensing
element and a further optical element when the intermediate layer
is subsequently coupled to the further optical element, with the
intermediate layer arranged between the optical element and the at
least one light sensing element, the at least one sensing element
receiving light in use from the further optical element.
[0077] In method or module according to the present invention and
preferred embodiments thereof as set out above, an optical element
other than a light sensing element may be used in place of the or
each light sensing element. For example a light source element
could be used instead of a light sensing element. Of course, the
direction of light transferral between the or each optical element
and the further optical element would have to be construed and
varied accordingly, so that for example in the case of using light
source elements as the optical elements, the or each optical
element would be optically coupled to the further optical element
for providing light to, not for receiving light from, the further
optical element. A method or module embodying the present invention
can thereby relate to an optical assembly in general rather than to
a light sensor module assembly in particular.
[0078] Advanced electronic interconnect packaging methods are
needed for applications which require individual or 2D arrayed
elements (i.e. sources or sensors) for large area
emission/detection. Applications include RFID' s, smart card
biometrics, flex displays, large area OLED (Optical Light Emitting
Diodes) lighting and medical sensor array imaging.
[0079] These applications require the development of smart
electronic interconnect solutions which support high fidelity low
cost, light weight connections to each element within an array such
that all elements are either individually or collectively
addressed.
[0080] Various deficiencies of the prior art are addressed by a
packaging embodiment of the present invention wherein a mechanical
assembly method to package elements in an N.times.M array format is
disclosed. An embodiment of the present invention will be primarily
described within the context of the integration and coupling of
photodetector elements to scintillator sources. However, it will be
appreciated by those skilled in the art informed by the teachings
herein that an embodiment of the present invention is also
applicable to any element such as a source where scaling in array
format is desired.
[0081] The module may be operable in a mode of operation in which
the elements cooperate in use to produce a combined output signal
indicative of an overall level of light falling on the
elements.
[0082] Each element may be arranged to make electrical connection
to the intermediate layer through the surface of the element that
is arranged to faced towards the intermediate layer. This leaves
the sides of the element substantially free, thereby enabling
adjacent elements to sit closely together to form a close-tiled
arrangement of the elements covering a large area.
[0083] Each element may comprise solid-state light sensing
circuitry.
[0084] Each element may comprise a silicon die.
[0085] Each element may comprise low-voltage circuitry.
[0086] Each element may be adapted to produce an amplified
electrical output signal which is substantially proportional to the
optical input signal.
[0087] The output signal may be an analogue output signal.
[0088] Each element may comprise high-gain light sensing
circuitry.
[0089] The gain may be greater than 10.sup.3.
[0090] The gain may be greater than 10.sup.5.
[0091] Each element may comprise Silicon Photomultiplier circuitry,
Avalanche Photodiode, PIN Photodiode.
[0092] Each element may have a substantially rectangular
footprint.
[0093] Adjacent elements may be arranged to abut each other.
[0094] The active area of each element may extend substantially to
the edges of the element.
[0095] Each element may comprise shallow junction circuitry having
electrical contacts on the opposed surface.
[0096] Each element may be prepared using a back thinning technique
on a light input surface.
[0097] Each element may be bonded to the intermediate layer.
[0098] The module may comprise additional circuitry for providing
additional functionality.
[0099] The additional circuitry may comprise processing circuitry
for processing signals received from the elements.
[0100] The additional circuitry may comprise control circuitry for
sending signals to the elements.
[0101] The additional circuitry may comprise interface circuitry
for interfacing with external apparatus.
[0102] The additional circuitry may comprise capacitance decoupling
circuitry.
[0103] Where the intermediate layer has a light input surface
facing the elements and an opposed surface facing away from the
elements, the additional circuitry may be mounted on the opposed
surface of the intermediate layer.
[0104] The additional circuitry may be low-voltage circuitry.
[0105] The SiPM may form an overall active area greater than 1
millimetre square in area
[0106] The SiPM may form an overall active area greater than 5
millimetre square in area
[0107] The SiPM may form an overall active area greater than 10
millimetre square in area
[0108] The tiled arrangement may form an overall active area
greater than 1 square cm in area.
[0109] The tiled arrangement may form an overall active area
greater than 5 square cm in area.
[0110] The tiled arrangement may form an overall active area
greater than 10 square cm in area.
[0111] Each element may comprise a light input surface arranged to
face towards the intermediate layer and an opposed surface arranged
to face away from the intermediate layer, and may be arranged to
make electrical connection to the intermediate layer through the
light input surface.
[0112] The module may be operable in a mode of operation in which
different groups of elements are selectable to produce different
output signals for those respective groups, whether at the same
time or at different respective times or a combination thereof,
where each group comprises one or more elements.
[0113] The module may be operable in a mode of operation in which
each group comprises a single element, so that separate output
signals are produced for the respective elements.
[0114] The module may comprise output circuitry operable to allow
the output signals to be read out individually or multiplexed and
read out sequentially as appropriate.
[0115] The module may comprise amplification circuitry to amplify
one or more output signals before they are passed outside the
module.
[0116] The module may comprise a connector for connecting to
control circuitry arranged on a separate substrate. Light sensor
apparatus may be provided comprising such a light sensor module and
the separate substrate on which the control circuitry is
arranged.
[0117] A method may be provided to optically couple a light source,
light sources or coupling element(s) to at least one detector
element or "tile" consisting of an array of detector elements.
[0118] An assembly may be provided comprising an intermediate layer
positioned between the source and detector elements.
[0119] An assembly may be provided comprising an intermediate layer
providing direct or indirect optical coupling and mounting means to
secure and align an optical source or coupling element to detector
element.
[0120] An assembly may be provided comprising an intermediate layer
consisting of electrical interconnection to address collectively or
individually the detector elements.
[0121] The intermediate layer may be a substantially planar
film.
[0122] The intermediate layer may form a printed circuit.
[0123] The intermediate layer may be rigid or flexible or both.
[0124] The intermediate layer may comprise a polymer or suitable
material such as silicon, glass, or dielectric film.
[0125] The intermediate layer may have sufficient optical
transparency for source emissions and detector responsivity.
[0126] The intermediate layer may not be optically transparent but
may be perforated with machined apertures of varying shapes and
sizes.
[0127] The sidewalls of the machined apertures may be angled and
metallised to improve the collection of light onto the
detector.
[0128] The perforated openings in the layer may be filled with
appropriate index match material or cookies to optimise coupling
and reduce refractive index difference between the detector and
source.
[0129] The intermediate layer may be unperforated, but may instead
have embedded optical layers such as waveguides and optical
elements such as gratings or mirrors to couple, transport and or
redirect the light signal between different elements.
[0130] The intermediate layer may range in thickness from thin
membranes to thick layers.
[0131] The intermediate layer may have fine metal traces with
single or multiple metal levels.
[0132] The intermediate layer may contain single or multiple
bondpad sites.
[0133] The intermediate layer may comprise a single metal layer
with single or multiple metal traces.
[0134] The intermediate layer may comprise a double metal layer
flex with single or multiple traces on both sides of the flex.
[0135] The intermediate layer may comprise of a multiple metal
layer flex with single or multiple traces.
[0136] The intermediate layer may comprise light sensing circuitry
and components.
[0137] The intermediate layer may comprise metal traces on the
intermediate layer facing the source which back reflect light not
impinging on the active area of the detector back to the emissive
source.
[0138] The intermediate layer when machined may enable the coupling
and attachment of fibres, waveguides, lights cones to be accurately
aligned and connected to the detectors an intermediate layer
comprising of perforated structures with pedesatals or stand-offs
to enable direct integration of coupling elements such as
fibres.
[0139] The intermediate layer may comprise perforated openings of
varying shapes and sizes to accommodate the accurate alignment and
fixturing of source or coupling elements to the detectors.
[0140] The intermediate layer maybe stiffened, for example around
the periphery of the circuit to provide specific areas of rigidity
where needed, examples of materials used include Cirlex with
200-300 .mu.m thickness.
[0141] The intermediate layer may comprise adhesives sites or
appropriate mounting features to align and/or lock the detectors
and sources in their respective position.
[0142] The source may consist of fibres, scintillators, photonic
crystal, quantum dots, lasers holy fibre, waveguides.
[0143] Coupling elements such as winston cones or adiabatic tapers,
scintillating fibers or wavelength shifted fibers may be
provided.
[0144] A plurality of sources may be coupled directly to multiple
detectors which are addressed electrically.
[0145] A plurality of sources may be addressed electrically and
coupled to a single source or plurality of sources electrically
connected.
[0146] A single source may be directly coupled to multiple
detectors in a hybrid assembly.
[0147] A single source may be directly coupled to multiple
detectors formed on single piece of Silicon (large area monolithic
chip).
[0148] A single source may be directly coupled to one or more
detectors in array.
[0149] A single source may be directly coupled to single detector
or summed detectors which are connected electrically.
[0150] Detectors elements may be attached electrically onto the
intermediate layer via wirebonds, flip-chip assembly, lamination,
printing or via a suitable replication processes.
[0151] A suitable bonding process may include bumps bonds e.g.
plated, stud or via pastes, adhesives or suitable conductive
materials.
[0152] A suitable bonding process may include ultrasonic or
thermocompression bonds involving direct metal to metal
contacts.
[0153] Multi-pin flex connector plus ribbon cable may be provided
for communications to readout boards located off chip.
[0154] The intermediate layer may have custom ASIC for readout
electronics directly integrated.
BRIEF DESCRIPTION OF THE DRAWINGS
[0155] FIG. 1, described hereinbefore, shows a
previously-considered Scintillator-to-PMT PET detection system;
[0156] FIG. 2 shows an arrangement not embodying the present
invention in which the PMT of FIG. 1 has been replaced by a SiPM
detector array;
[0157] FIG. 3 is an illustrative perspective diagram showing a
light sensor module embodying the present invention;
[0158] FIG. 4 illustrates an intermediate flex layer having
machined apertures and SiPM bonding sites according to an
embodiment of the present invention;
[0159] FIG. 5 is a cross-sectional view showing elements of a
detector module embodying the present invention;
[0160] FIG. 6 shows an assembled detector module having two SiPM
detectors coupled to a scintillator via an intermediate layer
according to an embodiment of the present invention;
[0161] FIG. 7 illustrates an intermediate layer according to an
embodiment of the present invention for use with a 5.times.5 array
of detectors;
[0162] FIG. 8 shows a track layout on an intermediate layer
according to an embodiment of the present invention for addressing
individual detectors; and
[0163] FIG. 9 illustrates an embodiment of the present invention in
which an intermediate flex layer is bent to conform to the
curvature of the output from a radial source.
DETAILED DESCRIPTION
[0164] As mentioned above, it is desirable to address the
integration of M.times.N arrays of SiPM detectors for one-to-one
coupling or combined detection with scintillators for applications
including but not limited to those described above. FIG. 2 is a
diagram showing a simple arrangement, not embodying the present
invention, in which the PMT detector implementation of FIG. 1 has
been directly replaced by a SiPM detector array implementation,
with direct optical coupling between the SiPM detector array and
the scintillator crystal block.
[0165] FIG. 3 is an illustrative perspective diagram showing a
light sensor module embodying the present invention. The light
sensor module comprises a plurality of light sensing SiPM detectors
mounted and arranged on an intermediate layer between the source
and the detectors. The intermediate layer in this example is a thin
film flexible printed circuit board based on a polyimide based
substrate.
[0166] Flex circuitry is well suited as an interconnect medium and
has become widely accepted for many packaging applications which
require light weight, low cost package solutions in space
constrained environments.
[0167] In this application, the flex layer is static in that it is
not bent into position for installation nor is it subject to
numerous bends as a result of mechanical movement. The thickness of
the flex is this example is 25 .mu.m (polyimide) and 20 .mu.m metal
combination (Cu/Ni/Au).
[0168] In this example, a 5.times.5 array of detectors are tiled
and mounted on the flex with a spacing between detectors of 100 to
200 .mu.m. For other applications, such as microarray readers a
N.times.1 array is required with a spacing between the detectors
which is greater than 100 .mu.m and typically 1 mm.
[0169] For this particular example where the detector pitch is
small, two styles of flex construction can be used (a) single-sided
flex circuits with copper conductor layers on a flexible dielectric
film; or (b) double-sided flexible circuit consisting of two copper
layers.
[0170] For high-density flex circuit technology using large array
sizes N>5, multilayer flex circuits are more appropriate
construction choice as the metal is buried and routed to the
outside of the circuit via multiple buried intereconnect layers. If
optical coupling efficiency is paramount, and if the flex substrate
does not provide sufficient transparency to the optical light to
provide a predetermined minimum required level of optical coupling
efficiency, the flex layer can be machined with a honeycomb or
lattice structure by laser machining or other appropriate methods
such as wet etch to allow maximum light transmission through the
apertures (windows) corresponding to the active area of the
detectors. This is illustrated in FIG. 4, which illustrates an
intermediate flex layer having machined apertures and SiPM bonding
sites (four per detector). As the region around the perforated
areas is delicate a backing film similar to "blue tape" in wafer
processing maybe used which provides mechanical support to the flex
layers at the assembly stage. This backing film examples can be
removed (peeled off) when the detector elements are assembled. The
backing film adheres to the flex with a tacky adhesive. This
adhesive can be removed chemically or left and used to attach the
flex to the scintillator source.
[0171] The perforations or windows or apertures can be infilled
with an appropriate index match material if losses are critical.
Materials include silicone rubbers for making optical joints
between detectors and sources such as plastic scintillators. The
silicone cookies are soft and flexible and can be made to conform
to contoured surfaces.
[0172] The light sensing elements can be arranged to cooperate to
produce a combined output signal indicative of an overall level of
light falling on the light sensing elements or several outputs
signals corresponding to individually or collectively addressed
detector signals.
[0173] This output signal or signals pass out of the through
electrical traces (not shown in FIG. 4) and flex connectors on the
intermediate layer to external circuitry for processing.
[0174] Each detector comprises a light input surface arranged to
face toward the intermediate layer and source. Each detector is
arranged to make electrical connection to the intermediate layer
via metallised bondpads on the flex. This is illustrated in FIG. 5,
which is a cross-sectional view showing different elements of the
detector module construction: the scintillator, perforated flex
(intermediate layer) and single SiPM detector. This enables
adjacent light sensing elements to sit closely together to form a
close-tiled arrangement of light sensing elements and results in a
large active area; this is illustrated in FIG. 6, which shows an
assembled detector module having two SiPM detectors coupled to a
scintillator via an intermediate layer. Example dimensions for this
assembly are indicated in FIG. 6.
[0175] The inclusion of the perforated flex printed circuit results
in an air gap formation between the source and the detector. This
thickness of this gap is determined by the thickness of the flex,
which can be of the order of 50 .mu.m for a single metal layer
flex.
[0176] FIG. 7 illustrates an example 5.times.5 array of detectors,
with metal layout based on single flex metal level. An example of
track layout to address individually the detector outputs for
one-to-one coupling to scintillator crystals for higher spatial
resolution is illustrated in FIG. 8; also shown is a 50 pin flex
connection for readout electronics. The detectors (not shown) are
mounted in this arrangement with a .about.100 to 200 .mu.m gap
between detectors. The gap is determined by the resolution of the
printed circuit but typically single metal traces with track widths
of the order of 30 .mu.m are feasible.
[0177] So that the SiPM readout electronics does not degrade
detector performance or resolution, a highly integrated "on-chip"
front end readout electronics is provided. This is achieved through
appropriate readout design, circuitry mechanics and packaging.
[0178] For readout design, several custom ASIC's prototype designs
are being developed for signal preamplification and shaping. This
research is at the development stage with early 18 channel ASIC
prototypes available for variable gain charge preamplification and
shaping (see, for example, B. Schumm, "Research and Development in
Front-End Electronics for Future Linear Collider Detectors", 10th
Workshop on Electronics for LHC and future Experiments, Sep.
13-17th; Boston USA).
[0179] In the example illustrated, the readout circuitry is located
"off-chip" where electronic readout boards are connected via a
ribbon cable which is directly connected to the tracks on the flex
via an appropriate multi-pin flex connector. Examples of such
connectors include "Flip-Lock" SMT/ZIF type flexible printed
circuit board connectors vertically, top contact or bottom contact
type. Alternatively, SMT electronics can be mounted directly on the
flex substrate but this is not an eloquent a solution compared to a
customised ASIC mounted directly onto the flex.
[0180] To address the detectors individually, as shown in FIG. 8,
two conductor traces are needed within the gap. There is a
trade-off between with the thickness of the flex (gap height
between source and detector) and the track width between the
detectors.
[0181] One option is to design a single metal layer flex (typically
35 to 40 .mu.m). Two conductor tracks between the gap will require
two metal traces with three spaces, which can be challenging with
the current state of the art. Alternatively, a two-layer flex could
be provided that uses both sides of the flex to run traces. This
allows a wider track on each side of the flex with trace widths of
the order of 35 .mu.m. This is one solution to having a .about.100
.mu.m gap. Based on state of the art, the thickness of the
two-layer flex would be .about.45 to 55 .mu.m. The advantage of the
second option is to minimize the gap between detectors and thus
improve the overall fill factor for the detector array.
[0182] For electrical interconnection, detectors typically have
either one topside contact and one backside contact or two
frontside contacts. To address a detector array e.g. N=4 or N=5
requires a minimum of two conductor traces between the detectors.
In the example shown, four 100.times.100 .mu.m die bondpads are
located at the four corners of the device. Two bondpads are used
for electrical contacts while all four bondpads provide mechanical
stability.
[0183] For this assembly the bondpads may be plated with sufficient
metal for electrical contact. Alternatively; a gold stud bump flip
chip assembly process maybe used to create conductive gold bumps on
the die bond pads. Both methods connect the die to the intermediate
layer with adhesive, ultrasonic or thermocompression assembly. The
advantage of stud bumps is that they require no under-bump
metallization (UBM), and thus does not require wafer processing
such as passivation. The disadvantage of this technique is that it
increases the gap height between source and detector which maybe
unacceptable for certain applications.
[0184] In this example, either a 35 .mu.m of gold stud bump or 5
.mu.m electroplated Ni followed by an electroless gold finish is
used to bump the die. The metallization of the thin film flex is
typically 10 to 15 .mu.m of copper on one or both sides finshed
with a NiAu layer (1-2 .mu.m in thickness).
[0185] One example of the bonding process involves flip-chip of the
detectors directly onto bonding sites (pads) located on the flex.
Several methods are envisaged to achieve this, for example: [0186]
solder bumps are deposited by plating, stud, ink-jet or appropriate
techniques. The thickness of the bumps can vary depending on
process as discussed above.
[0187] As described above, a novel method is set out for compact
packaging optical single or multiple photodetectors to an optical
source or other optical element. An array of detectors in a tiled
arrangement is assembled using a small form factor thin
intermediate layer between the source optical element and the
detector, which allows high levels of component integration and
scaling. An effective large area SiPM detector is provided and its
packaging overcomes the inherent mechanical and packaging issues
associated with conventional detector assembly and packaging.
[0188] The intermediate layers serves one or more of the following
functions: [0189] as an electrical interconnection layer to address
detectors (individually or collectively) [0190] as a mechanical
interface layer between detectors and source for coupling light.
[0191] as a substrate to mount readout electronics. [0192] as a
mechanical interface layer to isolate different areas of source for
optical response. [0193] as a means to improve dead space when
tiling detectors. [0194] as a means to tile a N.times.M or
N.times.N detector array together where N=1, M=1 or greater. [0195]
as a mechanical layer which provides consistent and precise
alignment of detectors with respect to the source optical element.
[0196] as a means to sum collectively or individually detector
response. [0197] as a means to mechanically attach the detectors to
the source via an adhesive layer.
[0198] In addition, although in the main examples shown and
described above the intermediate layer is substantially planar in
nature even when assembled into the final sensor module
arrangement, it is a highly advantageous feature of an embodiment
of the present invention that the intermediate layer referred to
above need not be restricted to planar sources and/or planar
detector arrays. By forming the intermediate layer of a flexible
material, it may be conformed and bent into various shapes and
configurations while still maintaining sufficient mechanical
strength and rigidity.
[0199] When the intermediate layer is regarded as a flexible
membrane that may be shaped, it forms a means to couple an optical
source to an array of detectors mounted on a non-planar surface, as
shown for example in FIG. 9. The detectors mounted on the
intermediate layer are thus able to follow the contour or profile
of the source (not shown).
[0200] The intermediate layer and detector array can be curved in a
manner so as to couple to the curvature of the field of view of a
radial source, for example. The source can incorporate front optics
such as a lens which creates a focal surface emission. A method for
manufacturing flexible detectors and carrier substrates to adapt to
the focal image is taught is U.S. Pat. No. 6,649,843 B2. Using this
approach, the detector element is thinned and bonded to a flexible
carrier substrate in order to adapt to the curvature of the field
of view. This approach would typically require the use of flexible
detectors with a maximum thickness of 20 .mu.m and a length to
width ratio of approximately 20-60.
[0201] For many cost-sensitive applications, it is desired to have
a robust mechanical solution which does not involve chemical
mechanical polishing (CMP) techniques for back thinning, isoplanar
contacts which are necessary for low contact forces and complicated
die handling procedures. An embodiment of the present invention
provides a technique which can enable high optical sensitivity as
well as using standard front side "non flexible" detector arrays
and traditional bonding die techniques such as thermocompression
bonds using flip-chip techniques.
[0202] Equally, an embodiment of the present invention is useful
for UV-sensitive detection systems by avoiding CMP processing to
remove dead, absorbing layers between the source and the active
depletion region which is necessary for backside detector
illumination for UV sensitivity.
[0203] A flexible intermediate layer is adaptable to the
configuration of contour of the spectral, temporal and intensity
profile of the radiation source. The detectors can be coupled to
the radiation source by mounting the detectors on or within the
flex intermediate layer.
[0204] Not only can the flex intermediate layer conform to the
boundary of the radiation source, but it can also adapt and conform
in a dynamic fashion to a changing boundary. The flex intermediate
layer is form fitting in that the properties of the intermediate
layer maybe elastic or plastic such that it can be stretched
reversibly or otherwise to the construction of the previously
fabricated radiation source. The flex intermediate layer
thicknesses may be kept sufficiently small so to allow it to
conform to the construction specifications of the radiation source.
The flex intermediate layer may be arranged to conform to the
housing in which the radiation source is mounted. The flex
intermediate layer can be a single or multilayered arrangement of
detectors. The flex intermediate layer can be wrapped around or
within the contours of the housing.
[0205] The source itself may be any one or more of a point source,
pixellated source on planar surface or on an arc, Lambertian,
Gaussian Source, laser, LED, incandescent light bulb, microcavities
(microdisks, microspheres, resonant cavity light emitting diodes,
and single-photon sources). It may be a solid, liquid or gaseous
material which emits light in different directions i.e. single,
bi-directional, or omni directional as a result of a radiation. It
may be manipulated using beam filters, expanders, concentrators,
collimation of light, redirection (minors, beam splitters),
diffracted (grating which give spectral profile) and refracted
(aspheric lens). It may have beam preshapers; curved surface which
provides radial signal over a wide acceptance angle, right angle
output or any shaped out so desired.
[0206] The boundary to which the detector array is be shaped may
conform to the beam output profile; intensity, temporal or spectral
at or at preset locations from the radiation source. The boundary
can be determined by the shape of the source housing e.g. lens. The
boundary can be determined by the beam profile at a preset location
from the source housing. The source boundary may be continuously
changing such as an electroactive polymeric lens.
[0207] The intermediate layer can conform by wrapping to the
housing, which is where the radiation is emitted. The housing
design can be any desired shape, for example tubular (e.g. duct,
pipe), cylindrical, oval, circular, polygonal, ring-shaped, arc
housing, or square.
[0208] Applications where a curved membrane of SPM detectors would
find great use include, but are not limited to: [0209] Channel
based detection systems where the detector array can be coupled to
conform to the curvature of the wall of the channel. Examples
include flow cytometry. [0210] Focal surface from an optical
imaging system. [0211] Whole Body/Animal Positron Emission
tomography system where the detector array lines the detector ring
in single or multiple layers for time of flight PET and depth of
interection measurements. [0212] Biomedical reader, e.g. where a
detector array wraps around a clear container. [0213] Point sensor
where detectors are mounted inside a rod for invasive sensing in
environments e.g. oil exploration, fluorescence in solutions.
[0214] An embodiment of the present invention allows standard
frontside detector illumination, electrical contacts on the
frontside side (i.e. the same surface as the active region of the
detector), good optical coupling between the detector and the
source optical element (e.g. scintillator), and large area
detection which is scalable and which is modular in nature. The
complexity of existing, known processes affect yield. An
intermediate layer according to an embodiment of the present
invention avoids complex assembly and mechanical stability
associated with the prior art, for example as described in U.S.
Pat. No. 6,117,707 and U.S. Pat. No. 7,038,287.
[0215] An embodiment of the present invention avoids at least one
of the following: [0216] elaborate post processing of the SiPM
detector for electrical interconnection. Examples include via
through hole etch and metallisation (plating) for through-hole
vias. [0217] complex and expensive techniques using backside
illumination which requires backthinning at wafer level. [0218] use
of large and small solder bumps for flip-chip assembly. [0219] use
of wirebonds and wirebond passivation which are fragile and not
mechanically robust for large detector arrays. In addition, the
passivation material usually polymer coatings suffer from yellowing
with age thereby degrading transmission properties of the detector
system. [0220] expensive ceramics carriers and glass lids.
[0221] A process embodying the present invention is highly
adaptable to large volume manufacturing; options include: an
automated pick and place process where detectors are serially flip
chipped onto the intermediate layer; and an automated reel to reel
process such as wirefilm bonding (see U.S. Pat. No. 6,857,459).
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